The aim of this study is to evaluate the side friction demand factor in loop ramps of the interchange facilities. The substantial exclusivity of these types of the ramps is the existence of the horizontal curves, simultaneously with the longitudinal grades. In our study, we have employed CarSim and TruckSim software packages, as the simulation tools. Vehicles used in simulation are: Hatchback and Sedan (as passenger cars), and Truck (as heavy vehicle). Simulation is performed for two various types of loops, including Curve-Curve-Curve (C-C-C) and Spiral-Curve-Spiral (S-C-S), in two different conditions (braking, and no-braking). The results of the study show that the side friction demand factor values recommended by AASHTO Green book (as a main geometric design guideline) are skimp and uncertain. For condition of no-braking, these differences in uphill and downhill states are 24% and 18%, respectively. For braking condition, the difference between simulation results and AASHTO values, in uphill and downhill are 124% and 135%, respectively. Based on the regression analysis of the simulation results, the side friction demand factor models are achieved for different conditions. The findings of the study verify the necessity of revising friction demand values, especially for design of interchange loop ramps.
